The major objective of this proposal is to examine the influence of the catecholamines, dopamine and norepinephrine, on water and electrolyte metabolism. The intrarenal pharmacology of infused dopamine will be studied in dogs and its effect upon reabsorption by the proximal tubule will be determined by micropuncture. Changes in this nephron segment will be correlated with alterations in renal blood flow, sodium excretion and phosphate excretion. Additionally, experiments will examine the physiologic importance of endogenous dopamine to the phosphaturia of volume expansion. Changes in plasma and urinary dopamine conjugation and excretion following volume expansion will be measured. The effect of intrarenal dopamine on phosphaturic response will be assessed by dopaminergic blockage in animals whose parathormone is controlled. Spontaneously hypertensive rats will also be studied to determine if the exaggerated natriuresis of hypertension is correlated with changes in catecholamine excretion. These studies will contribute to the understanding of the contribution of catecholamines to the regulation of salt and water balance.